Peavey XR-600C Mixer Head Noise

[Enzo]

O)K, so sitting there the amp hums, plugging into the power amp in kills the hum, an plugging into the graphic in kills the hum? So unplugging from the graphic in returns the hum? AND... the master volume control has no effect on the hum? That doesn't leave us much. Between the master vol control and the main put jack/graphic in jack is U24b IC. See if the output pin is sitting at some DC voltage other than zero. And of course verify the power pins.


And just to be sure, take a signal cord, plug into the power amp in jack, now the other end, plug it into the MON OUT jack. Hum? No hum?

[PepsiMoon]

Ok first off I was a little confused. Now.. With the main Amp Module sitting not hooked up to the master board or anything , there's no hum or " Noise"
When I plug in the Master Board, there's a hum "Noise". When I turn up the sliders on the EQ, Main Master, Reverb To Main, Tape/Aux Level controls. The "Noise" gets progressively louder as I advance these controls.
I checked U24b and found the + Vcc in was 15.89 VDC -Vcc in was -15.89VDC, the output pin was 0 VDC. After checking other IC's around the board, I found one that had DC on the output pin. This IC is located
between the "Reverb to Master" and "Reverb to Monitor" Pots, and had a reading of +2.17 VDC. I did notice that when I touched the case of the Main Master Pot, I got a noise much like touching the hot pin of an RCA jack
hooked up to an amplifier. Now, with the Amp on and the Master Board connected the EQ, Main Master, Reverb To Main, Tape/Aux Level controls turned up humming away,I plugged my guitar into the PWR AMP Input and the hum vanished, clean guitar sound. When I unplugged the guitar cord from the PWR AMP Input the hum returned. When I plugged my guitar into Graphic In the hum vanished once again, clean guitar sound.
With the amp humming away I took a signal cord and plugged it into the Mon. Out jack and into the Power Amp In jack, the humming stopped. So that's where I stand with this thing.I appreciate all of your help and I'm sorry for the confusion...Thanks , PepsiMoon
** I thought I would add, that even though the Master Board is unhooked which results in no noise, when I connect anything to the 400BH Module Driver Board input, I get the same noise.
I traced the plug going from the input of the driver board that connects to the Master board and found the + input and ground. I soldered in a female RCA jack, then connected one channel of my outboard carver pre-amp to it and you guess it! Humming noise!But had signal( Music) I ran pre-out of a Marantz 2226 to it, same noise, and had signal (Music) When I disconnected the RCA Jack the noise vanished**So maybe it's not the Master Board at fault here at all. My guess is there's a fault in the 400BH Driver board.**

[Enzo]

I doubt it. With everything connected, you can plug into the power amp jack - which is actually a circuit on the preamp - and the amp performs fine, right? SO if the fault was on the 400BH it would be there all the time, or it would magically know when you plugged into that jack.

Going in the graphic in jack runs signal through a bunch of more circuitry, which all seems to work.

The IC between those controls is U16, the reverb driver. I bet that 2v goes away when the reverb pan is plugged into the board.

Your graphic is clean, so center the controls and forget them. You mention a bunch of controls, master, reverb aux/tape that increase the hum. DO they do it independently? Or must the master be up first. IN other words, with the master on 5 turning the reverb up increases hum. But if you turn the mast6er to zero, can you still hear hum when the reverb is turned up? The Tape/aux goes onto the main bus, so does the reverb to main. SO if the master can turn to zero and kill the hum, we know the hum is before the master.

Are the ICs in sockets on this one? I am now suspicious of U24, and if socketed, it is easily swapped with a different one to see if it changes things.

[PepsiMoon]

Yes, The Master must be up before the other controls increase the " Noise" The IC's are all in sockets on this amp..Thanks ...PepsiMoon

[PepsiMoon]

That did the trick! I swapped it out with one on channel 4 ( which I'll never use anyway.) The Old SP3's wont handle a lot of really deep bass,so I tried to run a guitar cable from Monitor Out to my Behringer 450 watt bass head, to my 2-15" cabinet and got hummmm. So I grabbed a 12 foot RCA patch cable and soldered a 1/4" guitar jack on one end,and ran that from Tape Out on the PV to the Behringer, sounds great!!
As I was cleaning all of the input jacks and such with Deoxit, I noticed that the Aux In female + connector tab was bent on the inside, touching the ground tab. So I desoldered it and tried to bend the tab back into position and it broke off. Now to figure out why the Monitor Out has hum...I'm wondering, since this amp can run at 2 ohms if I could maybe find 2 PV 8 ohm folded horn Sub Cabs to hook up to the other outputs on the back of the SP3's? Thanks for all of your help and patience.. A Nearly Deaf, PepsiMoon..LOL

[Enzo]

Peavey Parts dept will have the exact jacks.

So your basic setup is hum free? Where does the monitor put hum? Plug a cord from MON OUT to power amp in, then apply signal to an input channel and send some to the monitor bus and bring up the monitor master, is the MON still hummy playing through its own amp? I suggest this test, because if you connect the MON out to some other amp, we COULD be facing a ground loop or shielding problem.

You have the thing open, might as well fix it right. replace the bad IC. These are old 4558s, which used to be all over. Nowdays we have 4560 an 4580 as more common, either would work. A common TL072 would be fine, or even a NE5532. Just about any DIP-8 dual op amp will work.

[PepsiMoon]

Peavey Parts dept will have the exact jacks.

So your basic setup is hum free? Where does the monitor put hum? Plug a cord from MON OUT to power amp in, then apply signal to an input channel and send some to the monitor bus and bring up the monitor master, is the MON still hummy playing through its own amp? I suggest this test, because if you connect the MON out to some other amp, we COULD be facing a ground loop or shielding problem.

You have the thing open, might as well fix it right. replace the bad IC. These are old 4558s, which used to be all over. Nowdays we have 4560 an 4580 as more common, either would work. A common TL072 would be fine, or even a NE5532. Just about any DIP-8 dual op amp will work.

Hi Enzo, well,still a little hum in the background but not as bad as it was. I'm thinking seriously about shelling out the $$ for a brand new jacks and IC's for the Master Board, and Mixer section ( With the exception of the XLR's they seem fine) just to be sure..I got the hum from my Behringer 450 watt bass guitar amp head when connected to the "Mon. Out" on the PV. However, when I ran an RCA jack to a male guitar jack adaptor from "Tape Out" on the PV to the same Behringer bass amp head, I got good clean signal. No Hum at all. Weird. What do the 4560's and/ or 4580's usually cost? I counted 15 of the 4558's on the mixer board, and have to remove the EQ on the Master Board to count all of them. I'm going to pack toilet paper around all of the pots today and give them all a good healthy shot of deoxit 5. Most all of them have dead spots, are scratchy and a few are really hard to turn.

[Enzo]

DOn't bother replacing a million ICs, that isn;t where your hum is coming from unless one has a DC offset. I usually expect to pay like 40 cents for one of those ICs.


Get a can of Deoxit D5 spray, and squirt up inside each control and spin it back and forth. I bet almost all if not all of them clean up just fine. DO that before ordering new pots. Spray some Deoxit on a Qtip and swab the jacks out well. Look at how black your Qtip is. Qtips are cheap, use as many as you need to. I bet that cures a lot of jack issues right there. Deoxit won;t hurt the circuit board.

As long as your boards are out of the front panel use your ohm meter to verify the grounds of the jacks are connected. One output might be hummier than another due to a lost ground connections. Check the solder under all jacks.